Cpr medium large transport unable to maintain cabin altitude had to divert to an alternate. The left pack had iced up and the right pack overheated trying to compensate.

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Attributes
ACN	150013
Time
Date	199006
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : jfk
State Reference	NY
Altitude	msl bound lower : 41000 msl bound upper : 41000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zny tower : phl
Operator	general aviation : corporate
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : atlantic enroute : other oceanic enroute airway : a300 enroute other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	150013
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : instrument pilot : atp pilot : cfi pilot : commercial
Experience	flight time last 90 days : 150 flight time total : 9600
ASRS Report	150012
Events
Anomaly	aircraft equipment problem : less severe
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : declared emergency none taken : anomaly accepted other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

Aircraft was 1.5 hours into the flight at FL410. The cabin temperature was continuing to increase even at maximum cool. We had selected cowl anti-ice on prior to entering an area of clouds and thunderstorm activity. 8-10 mins later we got a cooling turbine hot light on the opp side we were having a problem with. Following the checklist we turned off the affected pack, opened the isolation valve and immediately started to lose pressurization at a rate exceeding 2000 FPM. We immediately donned oxygen masks and asked for lower altitude from ny commercial radio. They were unable to clear us lower than FL390. We declared an emergency to get a lower altitude and diverted to bermuda 45 mins away. On the ground in bermuda it was discovered that the air conditioning unit for the cabin had iced up and severely reduced the flow of air. The fact that cowl anti-ice was on and the low flow of air through the iced up unit caused the one remaining unit to overheat. Once we selected it off we had very little pressurization.

Original NASA ASRS Text

Title: CPR MLG UNABLE TO MAINTAIN CABIN ALT HAD TO DIVERT TO AN ALTERNATE. THE LEFT PACK HAD ICED UP AND THE RIGHT PACK OVERHEATED TRYING TO COMPENSATE.

Narrative: ACFT WAS 1.5 HRS INTO THE FLT AT FL410. THE CABIN TEMP WAS CONTINUING TO INCREASE EVEN AT MAX COOL. WE HAD SELECTED COWL ANTI-ICE ON PRIOR TO ENTERING AN AREA OF CLOUDS AND TSTM ACTIVITY. 8-10 MINS LATER WE GOT A COOLING TURBINE HOT LIGHT ON THE OPP SIDE WE WERE HAVING A PROB WITH. FOLLOWING THE CHKLIST WE TURNED OFF THE AFFECTED PACK, OPENED THE ISOLATION VALVE AND IMMEDIATELY STARTED TO LOSE PRESSURIZATION AT A RATE EXCEEDING 2000 FPM. WE IMMEDIATELY DONNED OXYGEN MASKS AND ASKED FOR LOWER ALT FROM NY COMMERCIAL RADIO. THEY WERE UNABLE TO CLR US LOWER THAN FL390. WE DECLARED AN EMER TO GET A LOWER ALT AND DIVERTED TO BERMUDA 45 MINS AWAY. ON THE GND IN BERMUDA IT WAS DISCOVERED THAT THE AIR CONDITIONING UNIT FOR THE CABIN HAD ICED UP AND SEVERELY REDUCED THE FLOW OF AIR. THE FACT THAT COWL ANTI-ICE WAS ON AND THE LOW FLOW OF AIR THROUGH THE ICED UP UNIT CAUSED THE ONE REMAINING UNIT TO OVERHEAT. ONCE WE SELECTED IT OFF WE HAD VERY LITTLE PRESSURIZATION.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.